Various sources of mesenchymal stem cells (MSCs) have been tested as a treatment modality for inflammation-related diseases, such as inflammatory bowel disease (IBD), graft versus host disease, rheumatoid arthritis, type I diabetes, and multiple sclerosis. Newman et al. summarized that the mechanisms of action for the immunosuppressive effects observed in MSCs include both direct cellular contact, along with the secretion of soluble factors, such as transforming growth factor-β, prostaglandin E2, indoleamine-dioxygenase, nitric oxide, and tumor necrosis factor-a-stimulated gene-6 (Newman et al. (2009) Treatment of Inflammatory diseases with mesenchymal cells. Inflamm Allergy Drug Targets 8:110-123).
Recently, Ren et al. showed evidence that MSCs may arrest activated T cells in a graft versus host disease model via the secretion of proinflammatory factors and nitric oxide (Ren et al (2008). Mesenchymal stem cell-mediated immunosuppression occurs via concerted action of chemokines and nitric oxide. Cell Stem Cell 2:141-150). Additional evidence indicates that MSC immune-suppressive activity is localized at the sites of inflammation and regulated by cells and factors present in local microenvironment, indicating that greater MSCs homing and infusion close to inflamed sites may enhance therapeutic results.